In medium saucepan, bring 2 1/4 cups of water to a boil. Add the rice and 1/4 teaspoon of the sault, reduce to a simmer, cover and cook until the rice is tender, about 17 minutes.
Meanwhile, on a sheet of waxed paper, combine the flour, thyme, black pepper, cayenne, and the remaining 1/4 teaspoon salt. Dredge the chicken in the flour mixture, shaking off and reserving the excess. In a large nonstick skillet, heat the oil until hot but not smoking over medium heat. Cook the chicken until golden brown and cooked through, about 4 minutes. With a slotted spoon transfer the chicken to a plate.
Add the onion, bell pepper, and 1/3 cup of the broth to the skillet and cook, stirring frequently, until the bell pepper is crisp tender, about 4 minutes. Stir in the reserved flour mixture. Gradually add the remaining 1/3 cup of broth, the milk, and the mustard and cook about 3 minutes. Return the chicken to the skillet and cook just until warmed through, about 1 minute. Transfer the rice to 4 bowls, spoonthe chicken mixter alongside and serve.